1. Field of the Invention
The present invention relates to a dispensing head for a liquid or pasty product, as well as a dispenser fitted with this dispensing head and comprising a reservoir for the product to be dispensed, there being provided pumping means actuatable by a push button provided for causing a dose of the product to be dispensed. The reservoir has a variable volume and is constituted, for example, by a flexible pouch or by a rigid cylindrical reservoir provided with a follower piston. The dispenser is particularly intended for dispensing and applying a cosmetic, dermatological or food product, such as, for example, a lotion, cream, shampoo, liquid foundation or gel, but any kind of liquid or pasty product may be dispensed. Such a dispenser advantageously takes a compact form with a reservoir of small capacity ranging, for example, from approximately 10 mm to some hundreds of mm.
2. Description of the Related Art
A dispenser of the kind described above is known, for example, from EP-A-0 733 559 which has a retractable reservoir connected by a first valve to a chamber whose volume is variable under the action of a push button. This variable volume chamber is itself connected to the outside by a second valve. The push button has a body which, together with the piston joined to the reservoir, constitutes the chamber with a variable volume. The piston is provided with a central duct, its free end on the side of the chamber being surmounted by an elastomer part which performs both the function of a sealing lip and of a one-way shutter valve capable of opening towards the variable volume chamber in response to low pressure in the chamber.
Trials undertaken by the Applicant have shown that the valve in accordance with EP-A-0 733 559 has two drawbacks. First, adjustment of a sealing lip made of an elastomeric material sliding between two rigid sides is difficult to obtain, in particular when the piston is only a few mm in diameter. Second, it is difficult to ensure movability of the piston because, depending on their chemical composition, certain products have a tendency to distend the elastomeric material constituting the piston, the latter then expanding and jamming in the chamber, and/or deforming the valve.
The dispenser is known from Utility Model DE-U-94 19268 has a compression chamber with a variable volume communicating with a piston having a central duct for the product obturated by a one-way valve. The piston is inserted inside a feeder duct communicating with a reservoir containing the product. The valve is in the form of an annular elastic membrane whose central opening is obturated by a pin carried by the piston. The membrane is joined to a cylindrical sleeve fitted in an annular groove in which the upper end of the piston is provided. The sleeve with the valve is made of a single elastomeric part.
Such a design has several drawbacks, both from the point of view of its manufacture and the point of view of its operation: indeed, during the mounting of the piston, it is necessary to provide a first seal between the piston and the sleeve while ensuring the correct axial positioning of the membrane relative to the pin. In the absence of an accurate positioning of the membrane, the pump has leaks or the delivery is not constant.
Furthermore, a second seal has to be ensured between the feeder duct and the piston. Because of the mounting of the piston inside the feeder duct, the cross-section for the passing of the product is restricted, which leads to a loss of pressure, requiring a hard operation of the pump. If this passage cross-section is increased, a bulky pump is obtained which cannot be associated with a dispensing head intended to surmount reservoirs of a small capacity. In all, two steps are necessary for mounting the piston in the pump. In the absence of a leakproof mounting of the various above mentioned components, the functional reliability of the pump is compromised.